1. Field of the Invention
The present invention relates to a new type absorbent composite wherein a water swellable solid body, particularly consisting of particles of various sizes and shapes from powder to pellets is improved in functioning and handling characteristics. More particularly, the present invention relates to a highly absorbent composite composed of or containing an absorbent polymer as a water swellable solid body and having a shape entirely different from conventional absorbent materials and a capability of stably absorbing a liquid of much higher quantity than its own volume and to a highly absorbent composite mainly composed of the composite.
The highly absorbent composite of the present invention can widely be used in diapers for babies and adults, feminine hygiene products, products for handling liquid and solid wastes of animals, and medical blood absorbent products just like conventional highly absorbent products and thus is particularly useful as a super thin pulpless absorbent making the best use of the capabilities of a so-called absorbent polymer. In addition, the absorbent composite can be used for a cold insulator, water holding material, an anti-dewing material, covering material of submarine cables, material for preventing water related accidents.
In addition, the present invention relates to methods and apparatuses for making the absorbent composite and the composite mainly composed of the absorbent composite.
Moreover, the present invention relates to an absorbent sheet which provides also the leakage resistance of a conventional backsheet when the absorbent composite is used in absorbent products in combination with various sheet substrates, to an absorbent sheet which provides also the acquisition capability of a conventional topsheet when the absorbent composite is used in absorbent products in combination with various sheet substrates, and to an absorbent sheet which can be used alone providing also the capabilities of conventional backsheet and topsheet.
2. Prior Art
A main absorbent component used in an absorbent product, which absorbs water and liquid exudates, is composed of a combination of fluff type wood pulp and so-called super absorbent polymer (hereinafter referred to as the “SAP”). However, in recent years, in order to improve the distribution efficiency of absorbent products, to reduce the inventory and display space thereof, and to save natural resources, social needs for reducing the dimensions of otherwise relatively bulky absorbent products are becoming strong.
A means for making an absorbent product more compact and thinner, in a combination of SAP and pulp, would be to increase the content of SAP that has a higher absorbency than that of pulp by 2 to 10 times and accordingly decrease the content of pulp. Eventually, if the content of the SAP is made 100 percent, the thinnest and most compact absorbent product would be able to be obtained.
However, as the content of the SAP increases, when it absorbs water, so-called “gel blocking phenomenon” due to the characteristic of SAP occurs. Thus, the absorbent product does not work as designed. At the present time, it is said that the ratio of the contents of the SAP and pulp is at most 1 to 1. A structure in which the ratio of the contents of the SAP to pulp is 2 or higher to 1, or so-called pulpless in which the content of the SAP is nearly 100 percent is very difficult to achieve at the present time. According to the conventional concepts generally applied in the field of absorbent products, the term “pulpless” means that the ratio of the contents of pulp to the SAP is approximately 1 or lower.
So far, various attempts for the pulpless structure have been made. A fiber type or web type SAP is made by directly spinning into acrylic acid type fiber or partially hydrolyzing acrylic acid type fiber. Another method is to make a web type absorbent polymer by impregnating a web with a monomer such as acrylic monomer and then polymerizing the monomer applying ultraviolet ray or electron beam. Still other method is to make an absorbent polymer sheet by carboxymethylating a non-woven fabric of cellulose or the like and then partially cross-linking the carboxymethyl cellulose.
However, so far, no successfully commercialized examples have been reported because of high costs of raw materials and high capital investments involved.
Liquid exudates discharged from living bodies are very different from each other depending upon their environmental and living conditions, and the frequency of discharging is not constant among them. Therefore, absorbent sheets used in many kinds of absorbent products need, responding to varied environs, to exhibit stably the capability of absorbing quickly and frequently.
As described above, a conventional two component (pulp and the SAP) absorbent is capable of meeting the need of frequently absorbing to some extent by taking advantage of the temporary retaining by pulp of liquids and the stably retaining by the SAP of liquids. However, an absorbent product in which the content of the SAP is made high or the SAP alone is used in order to secure high absorbency has a serious drawback; upon a liquid being discharged at first the SAP starts to absorb it all at once and thus an initial absorbing is very speedy but as the discharging is repeated, the absorbing speed drastically decreases.